Turbofan comprising a system comprising flexible screens for closing off the bypass duct

ABSTRACT

A turbofan having a nacelle delimiting a duct for a bypass flow and including a fixed structure including a guide vane support with guide vanes, a mobile cowl movable in translation between an advanced position and a retracted position, arms, each one being mobile in rotation on the guide vane support between a stowed position and a deployed position and comprising a distal end and a proximal end, for each pair of adjacent arms, a flexible screen extending angularly between the two arms, and of which an exterior edge is attached to the guide vane support, and wherein the distal end of each arm is fixed along the interior edge, a link rod mounted articulated between the distal ends, actuators to cause the mobile cowl to move, and an operating system which moves each arm. Such an arrangement allows a reduction in weight.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the French patent application No.2000067 filed on Jan. 6, 2020, the entire disclosures of which areincorporated herein by way of reference.

FIELD OF THE INVENTION

The present invention relates to a turbofan which comprises flexiblescreens and a set of mobile arms mounted so as to be able to rotate inorder to block the duct for the bypass flow, and to an aircraftcomprising at least one such turbofan.

BACKGROUND OF THE INVENTION

An aircraft includes a fuselage, to each side of which is fixed a wing.Under each wing is suspended at least one turbofan. Each turbofan isfixed under the wing by means of a pylon fixed between the structure ofthe wing and the structure of the turbofan.

The turbofan comprises a motor and a nacelle that is fixed around themotor. The turbofan has, between the nacelle and the motor, a bypassduct in which a bypass flow flows.

The nacelle comprises a plurality of reversal doors, each one beingmobile in rotation on the structure of the nacelle, between a stowedposition in which it is not in the bypass duct and a deployed positionin which it is positioned across the bypass duct in order to redirectthe bypass flow towards a window which is in the wall of the nacelle andwhich is open between the bypass duct and the outside of the nacelle.

Thus, the bypass flow is redirected to the outside and more specificallytowards the front of the engine in order to generate reverse thrust.

Although reversal doors are entirely satisfactory, it is desirable tofind different mechanisms, in particular more lightweight mechanisms.

SUMMARY OF THE INVENTION

One object of the present invention is to propose a turbofan whichcomprises a flexible screen and a set of arms which are mounted so as tobe able to rotate in order to block the duct of the bypass flow.

To that end, a turbofan is proposed having a longitudinal direction andcomprising a motor and a nacelle, surrounding the motor, which comprisesa fan casing, in which a duct for a bypass flow is delimited between thenacelle and the motor, and in which a flow of air flows in a flowdirection, the nacelle comprising:

-   -   a fixed structure fixed to the fan casing and comprising a guide        vane support bearing guide vanes,    -   a mobile cowl able to move in translation, on the fixed        structure, in a direction of translation between an advanced        position in which the mobile cowl is positioned such that it is        moved close to the fan casing and an extended position in which        the mobile cowl is positioned such that it is moved away from        the fan casing so as to define, between them, an open window        between the duct and the exterior of the nacelle, and facing the        guide vanes,    -   a plurality of arms, each one comprising a distal end and a        proximal end which is mounted so as to be mobile in rotation on        the guide vane support about an axis of rotation parallel        overall to the longitudinal direction, wherein each arm is        mobile between a stowed position in which the arm is outside the        duct and a deployed position in which the arm is across the        duct,    -   for each pair of adjacent arms, a flexible screen extending        angularly between the two arms and adopting the form of a        portion of an annulus with an exterior edge having a large        radius and an interior edge having a small radius, wherein the        exterior edge is attached to the guide vane support rearward of        the guide vanes, and wherein the distal end of each arm of the        pair is fixed along the interior edge of the flexible screen,    -   for each pair of arms, a link rod, of which one end is mounted        articulated to the distal end of one of the arms of the pair,        and the other end is mounted articulated to the distal end of        the other arm of the same pair,    -   a set of actuators causing the mobile cowl to move between the        advanced position and the extended position, and vice versa, and    -   an operating system configured to move each arm from the stowed        position to the deployed position when the mobile cowl passes        from the advanced position to the extended position, and to move        each arm from the deployed position to the stowed position when        the mobile cowl passes from the extended position to the        advanced position.

Replacing the reversal doors and their drive mechanisms with theflexible screens and the set of rotationally-mobile arms allows areduction in weight. Furthermore, the presence of several screens meansthat, where necessary, only one screen needs to be replaced.

Advantageously, the flexible screen is made up of a structure offlexible mesh to which a flexible skin is attached.

Advantageously, between its proximal end and its distal end, each armcomprises a guide groove which extends between the two ends and in whichthere slides at least one slider secured to the flexible screen.

Advantageously, the nacelle comprises a plate in the shape of a portionof an annulus, secured to the guide vane support and on which the armsare mounted with the ability to rotate.

Advantageously, the operating system comprises:

-   -   a cam secured to an arm and having a tooth,    -   a groove, made on the mobile cowl and in which the tooth is        received, and wherein, when the mobile cowl moves, the tooth        follows the groove and rotates the arm secured to the tooth, and    -   for each arm, a transmission system which transmits the movement        of the arm to the next arm.

Advantageously, the transmission system comprises, for two adjacentarms, a connecting rod mounted articulated between the two arms, and thepoint of articulation of the connecting rod to each arm is offset withrespect to the axis of rotation of the arm.

The invention also proposes an aircraft comprising at least one turbofanaccording to one of the preceding variants.

BRIEF DESCRIPTION OF THE DRAWINGS

The abovementioned features of the invention, along with others, willbecome more clearly apparent upon reading the following description ofan exemplary embodiment, the description being given with reference tothe appended drawings, in which:

FIG. 1 is a side view of an aircraft comprising a turbofan according tothe invention,

FIG. 2 is a perspective view of the turbofan according to the inventionin the extended and deployed position,

FIG. 3 is a schematic representation of a turbofan according to theinvention, viewed in vertical section,

FIG. 4 is a perspective view of an embodiment detail of a transmissionsystem according to the invention,

FIG. 5 is a perspective view from behind of the transmission systemaccording to the invention, and

FIG. 6 is an enlarged view of detail VI of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, terms relating to a position areconsidered with reference to the direction of forward travel of anaircraft, as indicated in FIG. 1 by the arrow F.

FIG. 1 shows an aircraft 10 that comprises a fuselage 12, to each sideof which is fixed a wing 14 that bears at least one turbofan 100according to the invention. The turbofan 100 is fixed under the wing 14by means of a pylon 16.

FIGS. 2 and 3 show the turbofan 100 which includes a nacelle 102 and amotor 20 that is housed inside the nacelle 102. The turbofan 100 alsocomprises a fan casing 202. In FIG. 2, the motor 20 is shown in chainline as a cylinder.

In the following description, and by convention, X denotes thelongitudinal direction of the turbofan 100 that is parallel to thelongitudinal axis of the aircraft 10 oriented positively towards thefront of the aircraft 10, Y denotes the transverse direction that ishorizontal when the aircraft is on the ground, and Z denotes thevertical direction, these three directions X, Y and Z being mutuallyorthogonal.

FIG. 2 shows the turbofan 100, and FIG. 3 shows a schematicrepresentation in section of the turbofan 100.

The turbofan 100 has, between the nacelle 102 and the motor 20, a duct204 in which flows a bypass flow 208 coming from the air intake througha fan 300, and which therefore flows in the flow direction from front torear.

The nacelle 102 has a fixed structure 206 that is mounted fixed on thefan casing 202. The fixed structure 206 is made up, in particular here,of a front frame 210 mounted around the fan casing 202 and of outerpanels 212 fixed to the front frame 210 and forming an exterioraerodynamic surface.

The nacelle 102 has a mobile assembly 214 which has a mobile cowl 216which forms the exterior walls of the nozzle.

The fixed structure 206 also has a guide vane support 218 which takesthe form of a cylinder with perforated walls, between which sets ofguide vanes 221 are arranged. In this case, the guide vane support 218is attached to the front frame 210.

In the embodiment of the invention shown in FIGS. 2 and 3, the mobilecowl 216 has an exterior wall 217 which is cylindrical and whichsurrounds the guide vane support 218.

The mobile cowl 216 is mounted mobile in translation in a translationdirection globally parallel to the longitudinal direction X on the fixedstructure 206 of the nacelle 102.

The mobile cowl 216 is mobile between an advanced position (FIG. 3) anda extended position (FIG. 2) and vice versa. In the advanced position,the mobile cowl 216 is positioned as far forward as possible, withrespect to the flow direction, such that the mobile cowl 216 is movedclose to the outer panels 212 and to the fan casing 202 and thus forms acontinuous aerodynamic surface. In the extended position, the mobilecowl 216 is positioned as far aft as possible, with respect to the flowdirection, such that the mobile cowl 216 is moved away from the outerpanels 212 and from the fan casing 202 so as to define, between them, awindow 220 which faces the guide vanes 221 and opens between the duct204 and the outside.

In the advanced position, the mobile cowl 216 and the outer panels 212extend in line with one another so as to define the exterior surface ofthe nacelle 102. In the advanced position, the mobile cowl 216 ispositioned facing the guide vanes 221, and prevents the flow of air frompassing.

In the extended position, the mobile cowl 216 and the outer panels 212are spaced apart from one another and define, between them, the openwindow 220 between the duct 204 and the exterior of the nacelle 102.That is to say, the air from the bypass flow 208 passes through thewindow 220 to end up outside the turbofan 100, passing through the guidevanes 221.

In FIG. 2, the mobile cowl 216 and the guide vane support 218 are madein two parts that are symmetrical about a vertical plane XZ. These twoparts are mounted on beams of the fixed structure 206, in particularhere, a 12-o'clock beam and a 6-o'clock beam which fill in the spacesbetween the two parts that make up the mobile cowl 216 and the guidevane support 218. Of course, the number of parts making up the mobilecowl 216 and the guide vane support 218 may be different.

The mobile cowl 216 is made to translate by any appropriate means, suchas slideways between the beams of the fixed structure 206 and the mobilecowl 216.

The nacelle 102 also comprises a set of actuators (not shown) that movethe mobile cowl 216 in translation between the advanced position and theextended position and vice versa. Each actuator is controlled by acontrol unit, for example of the processor type, which controls themovements in one direction or the other according to the requirements ofthe aircraft 10.

Each actuator may, for example, take the form of a double-action jack(two working directions), of which the cylinder is fixed to the fixedstructure 206 and a rod is fixed to the mobile cowl 216.

The fan casing 202 and the outer panels 212 form the upstream boundaryof the window 220 with respect to the direction of flow and the mobilecowl 216 forms the downstream boundary of the window 220 with respect tothe direction of flow.

The nacelle 102 comprises a plurality of arms 250 having a proximal endand a distal end. At its proximal end, each arm 250 is mounted with theability to move in rotation on the guide vane support 218, on theperiphery of the duct 204 and about an axis of rotation parallel overallto the longitudinal direction X. Each arm 250 is thus able to movebetween a stowed position in which the arm 250 is outside of the duct204 and is held closely against the exterior edges of the duct 204, anda deployed position (FIG. 2) in which the arm 250 extends across theduct 204.

Overall, each arm 250 extends in a plane perpendicular to thelongitudinal direction X.

The number of arms 250 depends on the dimensions of the turbofan 100 andmore particularly on the dimensions of each part that makes up the guidevane support 218.

The passage from the stowed position to the deployed position is via acombination of the movement of the mobile cowl 216 and of the rotationof the distal ends of the arms 250 towards the inside of the turbofan100.

The nacelle 102 also carries an operating system (400, FIGS. 3 and 4)which moves each arm 250 from the stowed position to the deployedposition when the mobile cowl 216 passes from the advanced position tothe extended position, and moves each arm 250 from the deployed positionto the stowed position when the mobile cowl 216 passes from the extendedposition to the advanced position.

The nacelle 102 also comprises, for each part making up the guide vanesupport 218, and for each pair of adjacent arms 250, a flexible screen252 which can be seen transparently (in chain line) on the left in FIG.2. Each screen 252 adopts the overall shape of a portion of an annulusabout the longitudinal direction X, with an exterior edge having a largeradius and an interior edge having a small radius. Angularly, eachflexible screen 252 extends between the two arms of the pair. Theexterior edge is attached to the guide vane support 218 rearward of theguide vanes 221, and the distal end of each arm 250 of the pair is fixedalong the interior edge of the flexible screen 252.

Furthermore, in order to guarantee separation of the two distal ends inthe deployed position, for each flexible screen 252, namely for eachpair of arms 250, the nacelle 102 comprises a link rod 254, of which oneend is mounted articulated to the distal end of one of the arms 250 ofthe pair corresponding to the flexible screen 252, and the other end ismounted articulated to the distal end of the other arm 250 of the samepair,

FIG. 6 shows an enlargement showing the link rod 254. The articulationconnecting each end of the link rod 254 to the corresponding distal endpreferably takes the form of a ball-joint connection.

The flexible screen 252 is positioned in front of the arms 250 and thelink rod 254 with respect to the front of the aircraft 10.

When the arms 250 are in the deployed position, the flexible screen 252is also deployed and spread out between the guide vane support 218, andthe distal ends of the arms 250 form a barrier across the duct 204 whichopposes the flow of the bypass flow 208 which is then redirected by theflexible screen 252 through the window 220 and the guide vanes 221. Inthe deployed position, the interior edge sits around the motor 20 and,as a preference, each link rod 254 has a shape which conforms to theexterior shape of the motor 20.

Positioning the flexible screen 252 forward of the arms 250 and of thelink rod 254 allows the flexible screen 252 to rest on the arms 250 andthe link rod 254 and thus resist the bypass flow 208.

Operation thus involves, starting from the advanced/stowed position,commanding activation of the actuators to move the mobile cowl 216 fromthe advanced position into the extended position, which causes theoffsetting of the mobile cowl 216 with respect to the guide vane support218. During the course of this movement, the operating system 400 movesthe arms 250 from the stowed position to the deployed position, and thishas the tendency to deploy the flexible screen 252 across the duct 204.

In reverse, operation thus involves, starting from the extended/deployedposition, commanding activation of the actuators to move the mobile cowl216 from the extended position into the advanced position, which causesthe mobile cowl 216 to become superposed with the guide vane support218. During the course of this movement, the operating system 400 movesthe arms 250 from the deployed position to the extended position, andthis has the tendency to return the flexible screen 252 to the outsideof the duct 204.

The use of the arms 250 mounted so as to be able to rotate on the guidevane support 218, and the use of the flexible screen 252, makes itpossible to lighten the assembly compared to the use of reversal doorsof the prior art. Furthermore, the flexible screen 252 makes it possibleto adjust the efficiency and the area match which characterize a thrustreverser and the area match denotes the ratio between the nozzle outletcross section in direct-jet mode and the nozzle outlet cross section inreverse-thrust mode.

The flexible screen 252 needs to exhibit structural characteristics thatare sufficient for withstanding the forces generated by the bypass flow208 and needs to be flexible enough that it can be stowed against theedges of the duct 204 in the stowed position. According to oneparticular embodiment, the flexible screen 252 is made up of a structureof flexible mesh to which a flexible skin, such as a fabric for example,is attached.

Between its proximal end and its distal end, each arm 250 may comprise aguide groove which extends between the two ends and in which thereslides at least one slider secured to the flexible screen 252 so as toensure radial retention of the flexible screen 252.

FIGS. 4 and 5 show one particular embodiment of the operating system400. The guide vane support 218 in FIG. 4 is partially cut away in orderto reveal the insides.

In the embodiment of the invention depicted here, the nacelle 102comprises a plate 219 which is secured to the guide vane support 218,which takes the form of a portion of an annulus and on which the arms250 are mounted with the ability to rotate. The plate 219 extends insidethe guide vane support 218.

According to one particular embodiment, for each arm 250 a shaft 402secured to the arm 250 is mounted so as to be able to rotate at theproximal end, on the plate 219 and forms the axis of rotation of the arm250.

In the stowed position, each arm 250 is stowed above the plate 219.

The mobile cowl 216 comprises a groove 404 which is positioned, forexample, in the vicinity of the 6-o'clock or 12-o'clock beams.

The arm 250 closest to the groove 404 is equipped with a cam 406 thathas a tooth 408 which is received in the groove 404. In the embodimentof the invention presented here, the cam 406 is secured to the shaft 402and positioned on the other side from the plate 219. Of course,depending on the space available, it is possible to provide a cam 406 onseveral of the arms 250 and one groove 404 per cam 406.

As the mobile assembly 214 moves towards the extended position, thetooth 408 follows the groove 404 and a deviation of the groove 404causes a rotation of the cam 406 and therefore of the arm 250 secured tothe cam 406, about its axis of rotation, towards its deployed position,and vice versa.

The groove 404 has a shape which is suitable to allow the rotation ofthe arm 250 from the stowed position to the deployed position when themobile cowl 216 passes from the advanced position to the extendedposition. Conversely, the groove 404 has a shape which is suitable toallow the rotation of the arm 250 from the deployed position to thestowed position when the mobile cowl 216 passes from the extendedposition to the advanced position.

The operating system 400 thus comprises the groove 404, the cam 406,and, for each arm 250, a transmission system 502 which transmits themovement of the arm 250 to the next arm 250 so that the arms then movesimultaneously.

Thus, moving all of the arms 250 is relatively simple to implement anddoes not require actuators beyond those necessary for moving the mobilecowl 216.

The transmission system 502 comprises, for two adjacent arms 250, aconnecting rod 506 mounted articulated between the two arms 250. Thepoint of articulation of the connecting rod 506 to each arm 250 isoffset with respect to the axis of rotation of the arm 250. Thus, whenone of the arms 250 moves, the other arm 250 is driven in rotation bythe connecting rod 506.

In the embodiment of the invention presented here, the connecting rods506 are attached to the arms 250 via cams 504.

The invention has been more particularly described in the case of anacelle under a wing but can be applied to a nacelle located at the rearof the fuselage.

While at least one exemplary embodiment of the present invention(s) isdisclosed herein, it should be understood that modifications,substitutions and alternatives may be apparent to one of ordinary skillin the art and can be made without departing from the scope of thisdisclosure. This disclosure is intended to cover any adaptations orvariations of the exemplary embodiment(s). In addition, in thisdisclosure, the terms “comprise” or “comprising” do not exclude otherelements or steps, the terms “a” or “one” do not exclude a pluralnumber, and the term “or” means either or both. Furthermore,characteristics or steps which have been described may also be used incombination with other characteristics or steps and in any order unlessthe disclosure or context suggests otherwise. This disclosure herebyincorporates by reference the complete disclosure of any patent orapplication from which it claims benefit or priority.

The invention claimed is:
 1. A turbofan having a longitudinal directionand comprising a motor and a nacelle, surrounding the motor, whichcomprises a fan casing, in which a duct for a bypass flow is delimitedbetween the nacelle and the motor and in which a flow of air flows in aflow direction, said nacelle comprising: a fixed structure fixed to thefan casing and comprising a guide vane support bearing guide vanes, amobile cowl movable in translation, on the fixed structure, in adirection of translation between an advanced position in which themobile cowl is positioned such that the mobile cowl is moved close tothe fan casing and an extended position in which the mobile cowl ispositioned such that the mobile cowl is moved away from the fan casingso as to define, between them, an open window between the duct and theexterior of the nacelle, and facing the guide vanes, a plurality ofarms, each one comprising a distal end and a proximal end which ismounted so as to be mobile in rotation on the guide vane support aboutan axis of rotation parallel overall to the longitudinal direction,wherein each arm is mobile between a stowed position in which the arm isoutside the duct and a deployed position in which the arm is across theduct, for each pair of adjacent arms, a flexible screen extendingangularly between each pair of adjacent arms and formed as a portion ofan annulus with an exterior edge having a large radius and an interioredge having a small radius, wherein the exterior edge is attached to theguide vane support rearward of the guide vanes, and wherein the distalend of each arm of the pair of adjacent arms is fixed along the interioredge of the flexible screen, for each pair of adjacent arms, a link rod,of which a first end is mounted articulated to the distal end of one ofthe arms of the pair and a second end is mounted articulated to thedistal end of the other arm of the same pair, a set of actuators causingthe mobile cowl to move between the advanced position and the extendedposition, and vice versa, and an operating system configured to moveeach arm from the stowed position to the deployed position when themobile cowl passes from the advanced position to the extended position,and to move each arm from the deployed position to the stowed positionwhen the mobile cowl passes from the extended position to the advancedposition.
 2. The turbofan according to claim 1, wherein the flexiblescreen is made up of a structure of flexible mesh to which a flexibleskin is attached.
 3. The turbofan according to claim 1, wherein, betweenthe proximal end and the distal end, each arm comprises a guide groovewhich extends between the proximal and distal ends and in which thereslides at least one slider secured to the flexible screen.
 4. Theturbofan according to claim 1, wherein the nacelle comprises a plateformed as a portion of an annulus, secured to the guide vane support andon which the arms are rotatably mounted.
 5. The turbofan according toclaim 1, wherein the operating system comprises: a cam secured to one ofthe arms of the pair of adjacent arms, the cam having a tooth, themobile cowl having a groove in which the tooth is received, and wherein,when the mobile cowl moves, the tooth follows the groove and rotates thearm secured to the tooth, and for each arm, a transmission system whichtransmits the movement of the arm to the adjacent arm.
 6. The turbofanaccording to claim 5, wherein the transmission system comprises, for twoadjacent arms, a connecting rod mounted articulated between said twoarms, and wherein a point of articulation of the connecting rod to eacharm is offset with respect to the axis of rotation of the arm.
 7. Anaircraft comprising at least one turbofan according to claim 1.